Re: [tip: sched/core] sched: Fix performance regression introduced by mm_cid

[Linux regression tracking #adding (Thorsten Leemhuis)]

[CCing the regression list, as it should be in the loop for regressions:
https://docs.kernel.org/admin-guide/reporting-regressions.html]

[TLDR: I'm adding this report to the list of tracked Linux kernel
regressions; the text you find below is based on a few templates
paragraphs you might have encountered already in similar form.
See link in footer if these mails annoy you.]

On 20.06.23 10:14, Swapnil Sapkal wrote:
> 
> On 4/22/2023 1:13 PM, tip-bot2 for Mathieu Desnoyers wrote:
>> The following commit has been merged into the sched/core branch of tip:
>>
>> Commit-ID:     223baf9d17f25e2608dbdff7232c095c1e612268
>> Gitweb:       
>> https://git.kernel.org/tip/223baf9d17f25e2608dbdff7232c095c1e612268
>> Author:        Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
>> AuthorDate:    Thu, 20 Apr 2023 10:55:48 -04:00
>> Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>> CommitterDate: Fri, 21 Apr 2023 13:24:20 +02:00
>>
>> sched: Fix performance regression introduced by mm_cid
>>
>> Introduce per-mm/cpu current concurrency id (mm_cid) to fix a PostgreSQL
>> sysbench regression reported by Aaron Lu.
> [...]
> I run standard benchmarks as a part of kernel performance regression
> testing. When I run these benchmarks against v6.3.0 to v6.4-rc1,
> I have seen performance regression in hackbench running with threads.
> When I did
> git bisect it pointed to this commit and reverting this commit helps
> regains
> the performance. This regression is not seen with hackbench processes.
> Following are the results from 1 Socket 4th generation EPYC
> Processor(1 X 96C/192T) configured in NPS1 mode. This regression
> becomes more severe as the number of core count increases.
> 
> The numbers on a 1 Socket Bergamo (1 X 128 cores/256 threads) is
> significantly worse.
> [...]

Thanks for the report. To be sure the issue doesn't fall through the
cracks unnoticed, I'm adding it to regzbot, the Linux kernel regression
tracking bot:

#regzbot ^introduced 223baf9d17f
#regzbot title sched: performance regression in hackbench (partly solved
in -next by c1753fd02a00, partially caused by df323337e50)
#regzbot ignore-activity

This isn't a regression? This issue or a fix for it are already
discussed somewhere else? It was fixed already? You want to clarify when
the regression started to happen? Or point out I got the title or
something else totally wrong? Then just reply and tell me -- ideally
while also telling regzbot about it, as explained by the page listed in
the footer of this mail.

Developers: When fixing the issue, remember to add 'Link:' tags pointing
to the report (the parent of this mail). See page linked in footer for
details.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
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